* It's natural to grieve: Claudius acknowledges that grief is a natural human response to loss. He says, "It is a common form, in man and woman, to mourn the dead." This is a general truth, but it doesn't address Hamlet's specific and intense sorrow.
* Hamlet should think of his mother: Claudius suggests Hamlet should be less distraught because Gertrude, his mother, is also grieving. He says, "Your father lost a father; that father lost his son." This is a manipulative tactic, trying to redirect Hamlet's grief towards his mother's feelings.
* Time heals all wounds: Claudius states that grief will fade with time. He says, "Time is out of joint...But to persever in obstinate condolement is a course of impious stubbornness; 'tis unmanly grief." This is a common sentiment, but Hamlet's grief is rooted in more than just the loss of his father.
* Hamlet should think of his duty to the kingdom: Claudius reminds Hamlet that he has responsibilities to his country as a prince and he shouldn't let his grief interfere with those duties. He says, "For your intent in going back to school in Wittenberg, it is most retrograde to our desire."
While Claudius' arguments are meant to be comforting, they are ultimately superficial and don't address the real reasons behind Hamlet's deep distress. He doesn't acknowledge the possibility that Hamlet's grief is amplified by suspicion over his father's death, or the guilt he feels for his own inaction.